326 CLIMATIC CONDITIONS OF THE GLACIAL EPOCH. 



at the present time, it is natural to ask what changes, if any, take phice 

 either from year to year, from decade to decade, or from century to century, 

 in the amount and distribution of this frozen precipitation. Should it appear, 

 on examination, that such changes do occur; and that within the lifetime of 

 a single observer, or sometimes indeed within a yenv or two, the amount of 

 these variations is very considerable, it would seem that the question would 

 immediately be asked, Are these changes not necessarily the result of varia- 

 tions in the meteorological conditions, and may we not by examination of 

 the records of temperature and rain-fall, so accurately kept during later 

 years, be furnished with some information as to the amount and character of 

 the climatic changes accompanying these comparatively rapid fluctuations 

 of the glacial masses, by which we shall be assisted in forming an opinion as 

 to the nature and magnitude of those more important changes which we are 

 led to suppose must have coexisted with those greater developments of snow 

 and ice, tlie epoch of which is commonly designated as the Glacial ? 



A small amount of information as to what is going on at the present day 

 in glacier regions makes us at once acquainted Avith the fact that glaciers 

 are by no means stable things, that they are subject to changes of dimen- 

 sions, and that in some cases these changes take place with extraordinary 

 rapidity. It is also generally recognized by those who have made even a 

 superficial acquaintance with the Alpine ice-fields that they are and have 

 been, since they first began to be noticed and studied, subject to oscillations 

 of considerable amount; these, however, are by glacial geologists not usually 

 considered to be in any way connected with phenomena of the Glacial epoch, 

 but are supposed to be merely temporary fluctuations, it being assumed, as 

 a matter of course, that if any glacier is now diminishing in length and thick- 

 ness it will, at no distant date, acquire its former dimensions. 



It may be at once stated that by far the most interesting and important 

 fact which presents itself to us on entering this branch of our inquiry is this : 

 that during the last half-century all those glaciers throughout the world 

 with which we are sufficiently well acquainted to be able to speak positively 

 as to their changes of dimensions have been more or less rapidly and regu- 

 larly diminishing in size. This fact will be first considered, and as complete 

 a general statement made in regard to its main features as the material at 

 hand will permit. Some account will then be given of former oscillations 

 of the glaciers in those regions in regard to wliich we are so fortunate as to 

 have some records, scanty as tliev almost invarialjly are: for attention to 



